Ask DLS: What's your favorite mobile app at the moment?

But alas, not all apps are created equal; some are way, way better than others. Which leads me to today's Ask DLS question: What is your favorite mobile app at the moment?

We don't necessarily mean the latest craze; we'd like to hear about apps that have stood the test of time on your device, apps that are among the first you install on a new smartphones, apps that have earned their place on your home screen and in your heart.

So, what are some of these apps? Bonus points for links to screenshots in the comments!